Calibrating measuring system



1953 G. E. BEGGS, JR, ET AL 2,

CALIBRATING MEASURING SYSTEM 3 Sheets-Sheet 1 Filed July 1, 1949 INVENTORS GEORGE E. BEGGSMR. ALFRED W KOZAK BY I WM 5% ATTORNEYS 1953 G. E. BEGGS, JR., ET AL 2, 3,

CALIBRATING MEASURING SYSTEM 3 Sheets-Sheet 2 Filed July 1, 1949 o9 T 5 om mm mm mm mm M H mm NGM E Om EEK mm mm; M vw w m r ED T. W W as fin A a RF No. o 8 mm M 0 En E 5 w:

Dec. 22, 1953 G. E. BEGGS, JR. ET AL 2,663,855

CALIBRATING MEASURING SYSTEM Filed July 1, 1949 3 Sheets-Sheet 3 INVENTORS GEORGE E. BEGGS,JR. BY ALFRED W. KOZAK ATTORNEYS Patented Dec. 22, 1953 CALIBRATING MEASURING SYSTEM George E. Beggs, Jr., Warrington, Pa., and Alfred W. Kozak, Camden, N. J., assignors to Leeds and Northrup Company, Philadelphia,

Pa., a

corporation of Pennsylvania Application July 1, 1949, Serial No. 102,616

11 Claims.

This invention relates generally to measuring, indicating, recording, or controlling electrical, physical, chemical, or other conditions, and it relates more particularly to the sequ ntial measuring, indicating, recording, or controlling of a plurality of frequently changing conditions. Cer tain adjustments of the equipment to eliminate errors are made automatically in response to certain changes in the conditions being measured. The word measuring will be usel generically hereinafter to include indicating, recording, or controlling.

In general, errors in measurement may be detccted and appraised by using the equipment in which the errors occur to measure some known reference quantity. in accordance with the invention, and as an object thereof, the measur ment of a reference quantity serves not merely to detect and appraise errors in the measuring equipment but it results in eliminating such errors by the aforesaid adjustment. More spe cifically certain errors are eliminated by compressing or expanding the range of the indieating or recording apparatus by the amount necessary to eliminate the error when the indication or record is read against its usual fixed scale.

Attempts have heretofore been made to reduce errors in measurement by simultaneously measuring an unknown and a reference quantity with duplicate measuring apparatus. These attempts have not been wholly successful, however, because of changin differences in the duplicate apparatus which sometimes occur due to such causes as the unequal eitects of aging or" either batteries or electronic tubes. it is deemed preferable to employ a single measuring equipment and to transfer it from a reference quantity to the unknown quantity. This single-equipment system, however, presents several difficulties among which, in addition to the problem of transfer ring the equipment from one quantity to another, is that of storing during intervals between transf rs the error information obtained by measuring the reference quantity. Furthermore, these difiiculties are multiplied by the necessity in some cases of measuring quantities which change at random, or on a schedule not known in advance and not within the control of those operating the measuring apparatus. In other words, th re can be only a one-way flow of information from location. of the quantity being measured to the measuring apparatus, which automatically must accommodate itself to the different quantities.

An object of the invention is to transfer automatically a single measuring equipment, or portion thereof, alternately from a quantity to be measured to a reference quantity distinguishable therefrom by being outside the expected range of variation of the quantity being measured and, after at least a predetermined time, to transfer the equipment back to the same or another quantity to be measured. A further object of the invention is to store for an unlimited time, until the recurrence of a reference signal outside the aforesaid range of variation of the quantity to be measured, information as to the condition f the measuring equipment gained during the aforesaid predetermined time. The latter object is accomplished in accordance with the invention by adjusting a slidewire, during the aforesaid predetermined time in which a reference quantity is being measured, and leaving this slidewire undisturbed thereafter until another reference quantity is measured.

This invention is particularly applicable where a substantial distance, perhaps spanned by a radio link, intervenes between the quantity, or condition, to be measured and the indicating or recording apparatus. Since, in accordance with the invention, no control is necessary over the sequence of operations at the location of the unknown quantities to be measured, it is only necessary that, from time to time, a standard reference condition shall there be available and that this standard condition be in some respect outside the range of variation of the condition to be measured.

Other objects and advantages of the invention will be apparent from the following more detailed description thereof with reference to the accompanying drawings, in which:

Fig. 1 is a schematic diagram of measuring apparatus embodying the invention;

Fig. 2 is a schematic diagram of the apparatus shown in Fig. l, certain details thereof being omitted for clearness;

Fig. 3 is a chart useful in explaining the operation of the invention; and I Fig. 4 is a more detailed fragmentary schematic circuit diagram of a portion of the apparatus shown in Fig. 1.

The invention may best be described with reference to a typical application thereof. For this purpose a radiosonde system has been chosen wherein accurate measur ment is particularly diiiicult because of the need for extra .ely lightweight equipment, and because the equipment must remain unattended during the night of the unmanned balloon.

Referring to Fig. 1, a barometric switch [0,

u? preferably of the aneroid type, is adapted and arranged to connect successively thermometer ii, humidostat i2, and reference signal circuit 53 to transmitter i l, although a different sequence of connections to other measuring devices may be employed if desired. Thermometer l i has a. resistance dependent ;on .the temperature of the air surrounding the thermometer. Humidostat 52 has a resistance dependent on the humidity of the surrounding air. Reference circuit it includes a fixed resistance .outside the resistance range of thermometer ii and humidostat l2. Transmitter l l produces av radio-frequency signal modulated in frequency :byiithe resistance of the device connected-to it-bybarometric switch iii, the frequency-modulated signal being transmitted from antenna l5. .Eur ther details of the transmitter-modulator arrangement are contained in Patent No. 2,283,919

to Diamond and Hinman. Other suitable wellknown systems for producing a radio-frequency signal modulated in frequency in accordance with the magnitude of the condition to be measured may be employed if desired.

Transmitter M may be constructed for modu- H lation over any desired frequency range, but by way of example a range of 8 c cles per second to 200 cycles per second will be assumed and will be referred to for convenience as audio frequencies. The modulation of the transmitter preferably should be substantially linear so that the resultant audio frequency will be a uniform, relative measure of the unknown condition.

It is contemplated that the frequency band from 8 to about 175 cycles per second ordinarily shall be used for measurement, at different'times, of temperature, humidity, or other quantity, and that the range from about 1'75 to 200 cycles .per second ordinarily willbe reserved for the reference signal which, for example, may be assumed to be 190 cycles per-second. This result is achieved by making theflxed resistance of reference circuit 53 outside theresistance. range of thermometer El and humidostat it, as mentioned.

In Fig. 3 the line M-N represents the assumed reference signal of 190 cycles per secondand the line PQ, represents the nominal dividing frequency of 175 cycles per second betweenref erence signals, above, and measurement signals, below. It will be understood that areference frequency of 190 cycles is used as atypical example, but that the actual reference frequency may be anywhere within the above-indicated frequency range. that the line i N is at about 95% of the full range of movement of pen 25. Likewise the nominal 175-cycle point at which a switching operation occurs preferably will be so chosen that it, represented by line P-Q, is about 87% of the full range. An important advantage of the invention lies in its ability to change its voltage range to conform to various requirements without physically disturbing the range of pen '25 on paper 26.

The foregoing apparatus, items it, ll, l2, it, it, and iii may be carried by an unmanned weather balloon, by way of example. As the balicon ascends to some predetermined height at which it is desired to measure temperature, barometric switch it, having previously .beensuitably adjusted, connects thermometer l l' to transmitter it which results in a signal modulated at a frequency representing the air temperature at the predetermined :altitude. Thereafter, when Preferably it will be so chosen the balloon ascends to a higher altitude at which it is desired to measure humidity, barometric switch id connects humidostat E2 to transmitter i l thereby to transmit a signal whose modula- 5 tion frequency represents the humidity of the air at this predetermined altitude.

l/Vhen the balloon ascends to a still higher altitude at which it is desired to calibrate the equipment to prevent subsequent errors in measlU .urement due to changes which may have oclcurredsince the last previous calibration, barometric switch it connects reference circuit it to transmitter thereby to transmit a referencezor calibrating signal. Barometric switch is ill may-be adjusted to cause calibration of the equipment at any desired altitude but for corn 'venience it will be assumed that calibration oc curs after a humidity measurement and before "the next temperature measurement.

The signals transmitted by antenna l5 are receivedby antenna is and converted to audiofrequency signals by receiver ll, which may be of any suitable well-known type. The signals from receiver ll correspond exactly in frequency to those produced in the balloon by thermometer ll, humidostat i2, or reference generator l3, and they are converted to D.C. voltages proportional to their frequency by frequency meter l8, described in more detail hereinafter.

In one position of the switching arrangement to be described later, this D.-C. signal is applied to servo amplifier at which controls the operation of servomotor it to move contact 22 of slidewire is to make the voltage of contact 22 equal to that from frequency meter it. As used herein the word slidewire is intended to include any form of impedance having a voltage contact movable relative thereto. With the circuit thus balanced, the position of contact 22 is a measure of the D.-C. voltage output of fre quency meter 15 which is a measure of the audio frequency at which transmitter id is modulated, and this is a measure of-temperature or humidity, or it ,is the reference signal, depending upon which device is connected to transmitter i l by barometric switch it. Pointer 2S, driven by motor 2 l. and therefore moving with contact 22, indicates on scale 2 t temperature, humidityyor the reference signal. Pen 25 aiiixed to pointer 23 records this same reading on the record'chart 26 which is moved under pen 2% at a uniform rate by any convenient source of power, not

shown.

There has been described in general terms apparatus for measuring and recording temperature or humidity at various predetermined altitudes of a weather balloon. As thus far described these measurements might be subject to considerable error due to changes of barometric pressure, or the temperature of the apparatus, or to other factors, among which variation in battery voltage is most important due to the light-weight lowcapacity batteries used in the transmitting equipment employed in small balloons. For example suppose that thermometer ll, humidostat i2, and reference circuit is are not in themselves the source .ofany errors and that th servo system including motor it functions perfectly. There remain twoprincipal, potential sources of error. First, errors may occur in producing audiorfrequency modulation within transmitter i l. Second, errors may occur in converting these audiofrequency voltages to D.-C. voltages in frequency meter it. In accordance with the invention the voltage of slidewire as is varied to eliminate any errors arising in transmitter I4 or frequency meter 58. This elimination of errors depends largely upon the measurement of unknown quantities being subject to substantially the same errors as the measurement of the reference quantity. It follows that the invention in its broader aspects is applicable wherever it is possible to provide such a reference signal, the weather balloon and its radio link being merely a typical example of one application of the invention.

For a more detailed understanding of certain errors to be corrected in accordance with the invention assume that in a temperature of 40 F. thermometer I I causes transmitter I4 to produce a 100-cycle modulation of the transmitted signal and consequently 100 cycles applied to frequency meter i8 producing, say, a 30-millivolt output therefrom. Now suppose that at a later time a temperature of 40 F. resums in the same resistance of thermometer I I but due to reduced battery voltage in the weather balloon the transmitted signal is modulated at 110 cycles. The result would be a 10% error. Similarly, changes in conditions at the receiver might cause frequency meter I8 to produce 33 millivolts instead of 0 millivolts with a 100-cycle signal applied to it. Errors of the forgoing character can be detected if, from time to time, a known reference quantity is measured.

After the previously described temperature and humidity measurements have been recorded an altitude is reached at which barometric switch It connects reference circuit I3 to transmitter I4 whereupon the reference signal is recorded from B to C, Fig. 3, subject to the same errors as the preceding trace. When the change is me do from humidostat I2 to reference circuit I3 the modulation frequency of the radiated signal changes from, say, 100 cycles per second to 190 cycles per second. As this modulation frequency passes beyond the upper limit of those frequencies used to represent temperature or humidity, namely 175 cycles per second in the example chosen, motor 2! in following the modulation frequency rotates cam 2'! until cam follower 28 drops into slot 29 closing switch 35. The motor 2i continues to move cents ct 22 to a new position where its volttage will equal that of frequenc meter i8 with 190 cycles applied thereto. Slot 253 in. cam 2! is sufficiently long and so positioned that follower 25 will remain in it to close switch from about 1'75 cycles to about 200 cycles corresponding to a reasonable frequency range for the uncorrected reference signal. It will be apparent that the position of follower 25 relative to cam 27 may be varied, by any suitable well-known means, not shown, to vary the range of the reference frequencies, herein considered to be from 1'75 cycles to 200 cycles for convenience, any where above, below, or within the band of measuring frequencies. If the reference frequencies are thus positioned within the band of measuring frequencies, the width of the former band may be adjusted by varying the width of slot 29 in cam 21.

Referring to Fig. 2, the closing of switch 38 results in the closing of relay 3I after a predetermined time delay during which the 190-cycle reference signal is recorded, as mentioned. This closing of relay 3! closes for a short, predetermined time the relay 32 which, in closing, does two things. First, it connects the output of servo amplifier 20 to servomotor 33 thereby to adjust contact 34 of slidewire 35. Second, it connects the input of amplifier 20 to fixed point 36 whereupon slidewire 35, by varying the voltage applied to slidewire I9 from battery 37, is positioned to make the voltage at point 36 equal to the voltage from frequency meter 28 at the reference frequency of 190 cycles per second. It will be understood that batteries shown and described herein may be replaced, if desired, by any other suitable well-known electric power supply. Thus the voltage at fixed point 36, and at the corresponding point on slidewire I9, has been adjusted by means of a reference voltage to serve as a standard for subsequent measurement of quantities subject to the same errors as the reference voltage thereby eliminating the efiects of the errors as described hereinafter. During this ad justment period motor 2! which controls recording pen 25 is inoperative, except for a possible small transient force, and the trace from D to E (or D to E) Fig. 3, is recorded.

After the aforesaid short, predetermined adjustment period, relay 32 reconnects the output of servo amplifier 20 to servo motor 2%, and it reconnects the input of amplifier Eli to contact 22, thereby again to adjust contact 22 to the same voltage as the output of frequency meter I8 which output remains the voltage resulting from the reference frequency. Inasmuch as point 36 has previously been adjusted to this same voltage and the adjustment has not been changed, contact 22 will now be set to a point near the end of slidewire I9 at the same voltage as point 35, and pen 25 will record for an indefinite time the trace between and G, Fig. 3, this being the corrected reference record differing from the trace B to C by the amount of the correction.

When barometric switch H3 terminates the l-cycle reference signal and connects thermometer II to transmitter i i, air temperature will be measured and recorded in the way previously described, but this measurement and re cording of temperature will be done with a corrected voltage supplied to SliilGLJe iii due to the previously described readjustment of slidewire 35. Inasmuch as slidewire may be left stationary for an indefinite time, thereby retaining the result of the previous measurement of the reference quantity, this slidewire sociated voltage-supply circuit properly may be referred to as a memory device.

It will be apparent that the above mentioned adjustment of slidewire 35 serves to eliminate errors in the measurement of temperature or humidity which are also present in the measure ment of the reference signal when it is recalled that measurement of temperature and humidity is accomplished by comparing the respective output voltages of frequency meter iii to the total voltage of slidewire I9. In other words, the output of frequency meter I6 is determined to be a certain fraction of the total voltage of slidewire I9, the fraction being determined by the position of contact 22. This fraction is corrected for the reference signal by adjustment of slidewire 35, as described, and it will therefore be correct for other signals provided slidewire I5 and frequency meter It function linearly. Should either slidewire I9 or frequency meter I8 not be linear, second order errors will remain after the correction of primary errors by adjustment of slidewire 35, but the magnitude of such second order errors ordinarily will be small.

As the balloon ascends to higher altitudes barometric switch it will connect successively to transmitter 24, humidostat 12, referenc nerac e tor I3, and thermometer I! thereby alternately and its asreaches stop follower it drops into slot 45 of cam affixed to shaft ii thereby closing switch 1 .As mentioned, after a predetermined time de- .:lay. the. closing of switch tilactuates-relay 3i.

This. time delay is produced, as follows, referring to Fig. 1. Closing switch energizes relay 38 .by connecting it betweenthe B-l and B terminals of battery 53. Closing relay 38 energizes .motor. as from any suitable A.-C. power line it thereby rotating shaft ii, and crank 2 affixeol thereto against the tension of spring 33 to stop After a predetermined time, as 'crank' G2 ii-and connecting relay SE to battery 59. Sub- 'sequentl'y when relay 83 is deenergized by rota tion of cam-2i thereby'deenergizing motor 39, spring it rotates crank 2 backward against stop 23a thereby positioning motor 3% to repeat the time delay when it is reenergized. Other suitable'well-known time-delay de ices may be employed, if desired.

Energizing relay 3.! closes contacts 351; simultaneously supplying B+ voltage to electron tube 49, and to coil of relay 32; thereby energizing relay 32, and opens contacts Bic disconnecting grid of tube ts from cathode Eta so that capacitor 5i shunted by resistor after a time loses its charge from battery 53 to bias grid 59 to reduce the plate current of tube is substantially to zero thereby permitting relay 2:2 to re some its normal deenergized position. Whenever relay Si is deenergized grid 53 is connected to cathode sea charging capacitor 5% from battery 53 making tube it ready for further operation but simultaneously removing its B+ voltage to preclude operation until the operating cycle is repeated by reenergizing relay 3!. Capacitor 5i and resistor 52 preferably are of such values that r lay 32 will remain energized for about three seconds during which time servomotor 33 readjusts contact 34 relative to slidewire 35. Capacitor 5! may be about 1 microfarad and resistor 52 about 3 megohrns.

pen 25 records the corrected measurement of the reference signal represented between points F and G. This recording of the measurement of the reference signal terminates momentarily, at point G in Fig. 3, when barometric switch it disconnects reference circuit l3 from transmitter I l and reconnects thermometer H thereto.

However, it is desired to prolong thlsIGCOI'CL which may be used for reference purposesin interpreting other portions of the record on the chart 26, for two reasons: First, it is desired to provide a reference reading of adequate duration even if barometric switch iii operates to terminate the trace between points F and G after only a very brief time. Second, in case the weather balloon temporarily descends slightly,

or if for someother reason the reference signal should be interrupted briefly, it is desired to continue recording the reference signal without repeating the sequence of operations which other- -.wise would-be initiated by its momentary disappearance.

To this end, and. undercircumstances now to be described, the input circuit of amplifier 26 is connected between contact 22 and fixed point 36, at point G in Fig. 3, and left so connected until the reference signal disappears for at least a predetermined time. With this connection the voltage of point 3% will be measured and recorded and, since slidewire Etlhad been adjusted to balance the voltage of point 35 and the voltage due to the reference signal, this means that the reference signal record merely will be prolonged.

This prolonging of the reference record isv difficult to, achieve without spurious responses which would cause confusion in interpreting the record. For example, the uncorrected recording of the .reference signal might be too high, as shown MN as at point C or point E. It is not desired to initiate the above-mentioned prolonged recording at these decreases, but to initiate it only during the corrected recording of the reference signal as at point G or G. To distinguish between points C or E and points G or G, initiation of the prolonged recording is made to be contingent upon the sequential occurrence of two events, namely, the trace arriving at line M-N, Fig. 3, and thereafter departing from that line. Furthermore, to be effective those two events must occur at some time in the measuring cycle other than when the uncorrected reference signal is being measured; they will not be effective if they occur between pointsB and C or B and C.

To accomplish the aforesaid sequential occur- .rence of two events cam 51 driven by motor ii which moves with-cam 5?, is positioned at line MN, Fig. 3, which for convenience has been assumed to represent 190 cycles. Following is a description of the circuits actuated by this closing and opening of switch 5%, the circuits ignoring the closing of switch ti: if the uncorrected reference signal is being measured, but responding to its closing when the corrected reference .signal is being measured to prolong the record along the line M-N. Of course, the line MN ordinarily does not appear on chart 23, but it is convenient for purposes of explanation.

If the uncorrected reference signal is such that pen 25 rises to and beyond line Ml l immediately when reference circuit is is connected to transmitter i l by barometric switch it, as indicated atpoint Bin Fig. 3, the momentary closing of switch 59 when follower drops into slot 55 will not energize. relay 53 because contact 35a of relay 3! will be open and will remain open until point C is reached after a time determined by timer motor 39 as previously described. Switch 60 will again close after the uncorrected reference signal has. been recorded, as at point F at which time contact 3 la will have closed and relay 5% will be energized.

The .closingof switch so at point P, contact old ,now being closed, results in certain circuit changes preparatory to the subsequent opening of the same switch when the reference signal is terminated by barometric switch It at point G. After the aforesaid preparatory circuit changes, opening switch till will accomplish two things. First, by causing relay St to be energized it will transfer conductor ts from the output of frequency meter is to fixed point 36 thereby causing servo motor iii to balance the voltage of contact 22 against that of fixed point 36 and returning pen 25 to the corrected reference signal represented by line l\ ll-l'. Pen 25 will be returned to line MN so quickly that its departure and return are represented by a single line HG or H'G'. Second, it will start motor E? which subsequently, at po nt I, t rniinates the recording of the corrected reference signal and restores the system to its normal condition to record whatever signal follows the reference signal.

The above mentioned preparatory circuit changes start with the closing of switch 60 at point F to energize relay 58 through contact ills, now closed, thereby closing contact 58a and energizing relay i through relay 53, which is in its normally closed position. Energizing relay 6| does three things. First, contact Bid in parallel with contact Eda closed and when once closed it serves to complete the circuit to maintain relay 8! energized even after relay 58 is deenergized to open contact 58o. Second, closing contact 611) prepares relay ed for being energized when either contact 53d or contact bib is closed. Third, closing contact tic prepares motor 6?, and relay 62 in parallel therewith, for being energized when either contacts or 62a are close Energizing relay 58 also closes contact 5329 to apply B+ voltage to relay 53 through normally closed contact t le in readiness for the subsequent energizing of relay 53 by electronic tube t5 when the latter is rendered conductive by switch 69 connecting its grid ii to its cathode 1'2. Thus relay E3 is energized at point I" to terminate the sequence.

Energizing relay 5% also opens contact 58c. As mentioned, when relay 6! is energized contact bio closes and would thereby start motor 6? except that contact 550 opens to delay starting of motor until relay 58 is deenergized. Likewise, energizing relay opens contact 58d to delay energizing relay t l (through contact Slb) until relay 58 is deenergized. This completes the description of the aforesaid preparatory circuit changes in readiness for a description of the deenergizing of relay 58 and the resultant circuit changes.

When the reference signal is terminated by barometric switch it at point G (or point G), motor 3i moves pen downward in an attempt to balance the voltage of contact 22 to the voltage from frequency meter it with a signal proportional to temperature applied thereto. This downward movement of pen 25 is accompanied by rotation of cam 5'! to open switch 6i! and deenergize relay 58. This deenergizing of relay 58 results in the immediate interruption of the downward movement of pen 25 since, with the circuits prepared as above described, deenergizing relay 58 results in energizing relay E4 to cause motor 2| to balance the voltage of contact 23 against that of fixed point 3% thereby moving pen 25 back to the line l /I-ll in Fig. 3, closing switch 59 to reenergize relay 58.

The aforesaid deenergizing of relay 58 starts motor ill thereby to terminate the sequence, after a predetermined time, as follows: Deenergizing relay 58 closes contact sec thereby connecting relay EZ and motor tl to power line 48. This closes 10 contact 62a which is in parallel with contact 580 and maintains operation of motor cl by keeping relay 5?. energized despite the above-mentioned prompt reenergizing of relay 5% at point G. Energizing relay 62 also closes contact 5229 in parallel with contact to maintain relay dd energized even when relay is reenergized.

Motor 1! continues to rotate shaft and cam 88 affixed thereto until crank carried by shaft l3 meets stop l5 thereby stalling motor This rotation of cam 68 throws switch to thereby doing two things. First, it deenergizes relay 5 by opening its return circuit including contacts etc and Bib. The result of deenergizing relay depends upon the signal then being applied to frequency meter iii. If barometri switch it should cause the reference signal again to be applied to frequency meter It during the interval between point G and I and to remain so applied until after point I, motor 2; will remain stationary and switch so will remain closed until another to mination of the reference signal whereupon follower 55 leaving slot 55 in cam 5? opens switch 60 to repeat the cycle of operations that prolong the recording of the reference signal. However, if a lowerfrequency, temperature signal, for example, is being applied to frequency meter 15 when relay is deenergized, motor 21 wl move contact 22 downward thereby opening switch This opening of switch Ell immediately after relay t l has been deenergized, makes the oil uit ready for norm l operation to measure and record whatever signal follows the reference signal as described more fully hereinafter.

The second effect of throwing switch at point I is immediately to one: ize relay by connecting grid II to cathode E2 of eelctro' c tube and this takes place whether or not a reference signal is present. Energizing relay deenergizes relay 6! to open contact tic to deener ize motor ill and relay E2 whereupon spring it rotates motor El backward until crank 15 meets stop it thus restoring the motor to its initial condition.

This backward rotation of motor ill b spring It results in the immediate actuation of switch 69 to disconnect grid it from cathode i2. this disconnection were allowed immediately to bias tube 65 suiilciently to deenergize relay 53 thereby to energize relay iii before motor 25 had time to open switch to, energizing relay 6i would again start motor 57 to repeat the sequence over and over. To make sure that relay remains energized long enough for switch to open to terminate the sequence, capacitor id is so arranged that it must be charged through resistor '53 from battery TI to bias grid ll sufficiently negative to render tube 65 simiciently nonconductivs to deenergize relay 63. Resistor 79 may be about 2505330 ohms and capacitor about V2 microfarad.

Referring to Fig. 4 for a more detailed description of frequen y meter a sinusoidal voltage from receiver ii is applied to input tor lnals and a 11-0. voltage proportional in amplitude to the frequency of this input voltage is produced at output terminals 8 i. First, electronic tube 82 converts the sinusoidal voltage at terminals to a substantiall square wave as follows. Resistor 83 limits the amplitude of the positive lobes of the sine wave applied through capacitor St to grid 85 across grid leak A 3+ voltage of around 200 volts from any suitable ll-C. source is, in the absence of a signal at grid reduced to about 10 volts at plat s? by resistor Screen grid 89, by-passed by capacitor also normally is at about 10 volts supplied from 53+ through "ii resistor 9!. The negative lobe of the sine-wave voltage at terminal as drives grid 85 far beyond the plate-current cutoff point so that only the middle portion of the sine wave appears in amplified form at plate 81, and this middle portion is substantially a square wave.

lectron c tubes 92 and 83 form a multivibrator circuit or" a type which restores itself automatically in a predetermined time after being triggered by a voltage applied to one of its electrodes. The square-wave voltage from plate Si is differentiated by capacitor 9t and resistor 95 resulting in two short pulses for each cycle, one of positive polarity and the other of negative polarity. Depending upon the values of resistor as and of resistor 95 and battery 8'5, pulses of one polarity, but not both, will cause tube 92 to change its conductivity from full to substantially zero conductivity. Simultaneously the conductivity'of tube t3 will be changed oppositely by a pulse passed through capacitor 93 to grid 89 across resistor 553. After being triggered by a pulse from plate 37, the conductivity of tube 82 resumes its normal condition after a short period of time determined for the most part by the values of capacitor es and resistor mil. Capacitor 98 may be about 0.0001 mid. and resistor lei] about 1 megohm. The varying voltage across resistor lill is transmitted to grid 99 through capacitor 98 and the oppositely varying voltage across resistor is? is transmitted across resistor I95 to grid 33 of electronic. tube Hid through capacitor IE5. Resistor lid decreases the B+ voltage to an appropriate value for tube its.

Thus the multivibrator including electronic tubes 92. and 93 produces pulses all having the same predetermined duration, one pulse being produced for each cycle of the voltage applied to terminals Bil. These pulses appear across cathode resistor it?! and are averaged in the circuit comprising resistor H88, reactor Hi9, capacitor iii reactor iii, capacitor H2, and resistor H3. Thus by averaging pulses of a predetermined length occurring at the same frequency as the signal'to be measured, there is produced at terminal iii a D.-C. voltage proportional to the frequency of the signal applied to the terminals as.

It is unnecessary to give typical values for all of the circuit components associated with tubes 82, 92, and as since, in accordance with the invention, these circuits are used in well-known ways for well-known purposes. It is desired that the output voltage at terminals 8! shall be as nearly as possible a linear function of the frequency of the voltage applied to terminals 88. With 10o microsecond pulses produced by the multi-vibrator including tubes 92 and es, and with audio frequencies in the range used herein by way of example, the following values of output-circuit components are preferred.

Resistor iiii 5,009 ohms. Resistor m8 500 ohms. Reactor Hi9 150 henries. Capacitor iii? l6 mid. Reactor iii 150 henries. Capacitor M2 Smfd. Resistor ii3 5,000 ohms.

There has been described apparatus for successively measuring temperature, humidity, and a calibrating signal. In as much as these successive operations occur at predetermined altitudes, determined by barometric switch it, it is apparent that each change from one operation to another is an indication of the altitude of the balloon at the time the change is made. To indicate and record the altitudes at which calibration occurs counter H5, which may be any suitable well-known type such as a Veeder counter, is activated by cam follower 28.

There has also been described a cam-andfollower arrangement (cam 2i and follower 28) for initiating recalibration of the measuring equipment whenever cam 2i and slidewire it reaches a predetermined signal from the quantities being measured. In other words, recalibration is initiated whenever a voltage (say, that from frequency meter it) reaches a predetermined value. It will be apparent to one skilled in the measuring art that, instead of the cam and follower arrangement, an electronic circuit responsive to a predetermined voltage to actuate relay 38 might be provided to achieve the desired result of automatic recalibration in a circuit in which signals proceed from the location of'the quantities being measured to the indi ating or recording apparatus, but not in the reverse direction.

It will be understood that as used herein the expression servo system includes a system in which a servo amplifier, such as amplifier 2%, may operate with either of two servomotors, such as motor 25 or motor 33, together with necessary feed-back circuit.

While a preferred embodiment of the invention has been shown and described it is under-- stood modifications thereof may be made within the spirit and scope of the appended claims.

What is claimed is:

1. In combination, a conversion system for producing electrical signals having magnitudes representative of the magnitudes of a plurality of predetermined conditions, said system including a controller for producing a succession of said signals in predetermined sequence which are respectively representative of said plurality of conditions, a balanceable network including a calibration slidewire and associated contact relatively adjustable with respect to each other and a measuring slidewire and associated contact relatively adjustable with respect to each other, a servo system including a selector switch for selective relative adjustment between said calibration slidewire and its associated contact and between said measuring slidewire and its associated contact, said network having an input circuit for application thereto of said electrical signals from said conversion system, means oper able upon application to said balanceable network of a signal representative of a selected one of said conditions for operating said selector switch for relative adjustment between said calibration slidewire and its contact by said servo system to balance said network, said selector switch sub sequently being operable to connect said servo system for adjustment ofsaid measuring slidewire relative to its contact to rebalance said network.

2. In apparatus for measurin unknown quantitles in relation to a reference quantity having similar characteristics and being subject to sire ilar measuring errors, the combination which comprises a conversion system for producing a signal voltage representative of a selected one of said quantities, the signal voltage from said reference quantity difiering from the signal 13- ages from said unknown quantities, said con sion system being operable at diiierent times to produce signal voltages representative of both unknown quantities and said reference quantity;

ind a balanceable network including a measurng slid-ewire and a voltage supply therefor, a calibration slidewire for varying the voltage from said supply to reduce said errors, and a servo system for selectively adjusting said measuring slidewire in response to said signal voltages; said balanceable network comprising a voltage-sensitive selector system operable in response to said referencequantity signal voltages to connect said servo system for adjustment of said calibration slidewire, said selector system being operable in response to said unknown-quantity signal voltages to connect said servo system for adjustment of said measuring slidewire in measurement of said unknown quantities.

3. In apparatus for measuring an unknown quantity in relation to a reference quantity havi g similar characteristics and being subject to similar measuring errors, the combination which comprises a conversion system for producing a signal voltage representative of a selected one of said quantities, the signal voltage from said reference quantity from the signal voltage from said unknown quantity, said conversion systern being operable at different times to produce signal voltages representative of both said unknown quantity and said reference quantity; and a balanceable network including a measuring slidewire and a voltage supply therefor, a calibration slidewire for varying the voltage from said to reduce said errors, and a servo system for s lectively adjusting said measuring slidewire in response to said signal voltages; said balancenetwork comprising a voltage-sensitive selector system operable in response to said reirence-ouantity signal Voltage to connect said servo system for adjustment of said calibration slidewire, selector system being operable in response to said unknown-quantity signal volt age to connect sai servo system for adjustment or" said measuring slid-ewire in measurement of said unknown quantity.

i. In combination, a balanceable network including a calibration slidewire relatively adjustable with respect to its associated contact and a measuring slidewire relatively adjustable with respect to its associated contact, a servo system including a selector device for selectively adjusting relatively said slidewires and associated contacts in normal position connecting said servo system for adjustment of said measuring slidewire, said network having an input circuit for receiving signals of a predetermined character representative of the magnitude of a condition under measurement, and means operable upon the application to said network of a signal resulting in the movement of the measuring slidewire to a predetermined position for operating said selector device for transfer or" control of said servo system to said calibration slidewire for relative adjustment thereof to balance the network.

5. In a measuring system including a balanceable network having as one circuit component a calibrating impedance and as a second circuit component a measuring impedance and means for selectively adjusting one of said impedances to rebalance the network, the combination therewith of a selector system for changing the connection or" said adjusting means first to one and then to the other or said impedances, and means for controlling the operation of said selector system operable upon the application to said balanceable network of a signal of predetermined magnitude for shifting the connection of said adjusting means from one of said impedances to the other of said impedances.

6. In an apparatus for measurin unknown quantities in relation to reference quantities having similar characteristics and being subject to similar measuring errors, a conversion system for producing a signal voltage representative of a selected one of various quantities, the signal voltages from said reference quantities differing from the signal voltages from said unknown quantities, said conversion system being operable at difierent times to produce signal voltages representative of said unknown quantities and of said reference quantities, the combination of a balanceable network including a measuring impedance, a voltage supply therefor, and a calibrating nnpedance for varying the voltage from said supply to reduce said measuring errors, said network including a servo system for selective adjustment of said impede-noes, a selector system for connecting said servo system to one of said. impedances, and means responsive to a signal voltage of predetermined character for changing the connection or" said servo system from one of said impedances to the other of said impedances in avoidance of said errors in the measurement of said unknown quantities.

'7. In an apparatus for measuring unknown quantities in relation to reference quantities having similar characteristics and being subject to similar measuring errors, a conversion system for producing a signal voltage representative of a selected one of various quantities, the signal voltages from said reference quantities diiiering from the signal voltages from said unknown quantities, said conversion system being operable at different times to pr duce signal voltages representative of said L lknown quantities and of said reference quantities, the combination of a balanceable network including a measuring impedance, voltage supply therefor, and a calibration impedance for varying the voltage from said supply to reduce said measuring errors, said network including a servo system for selective adjustment of said impedances, a selector system for connecting said servo system to one of said impedances, and means responsive to a signal voltage outside the normal range of signal voltages from said unknown quantities for changing th connection of said servo system from one of said impedances to the other of said iinpedances in avoidance of said errors in the measurement of said unknown quantities.

8. A radiosonde measuring system comprising a meteorological measuring unit, a reference unit, a radio transmitter, a barometric switch for connecting said units successively to said transmitter at predetermined altitudes of said switch, a radio receiver for receiving signals from said transmiter, the output of said receiver being a voltage arying with the magnitude of the said quantity being measured, a measuring slidewire and associated contact and a voltage supply therefor, a calibrating slidewire and associated contact for varying the voltage from said voltage supply, a voltage divider connected across said measuring slidewire, a servo system including an amplifier and a switching arrangement therefor, said switching arrangement in one position thereof connecting said measuring slidewire and said receiver output in series opposition across an input circuit of said amplifier and connecting the output of said amplifier to cause said servo system to adjust relatively said measuring slidewire and its associated contact output of said voltage dividerequal to saidreceiver output, a cam movable with said contact associated with said measuring slidewire for shifting said switching arrangement from said first-named position thereof to said secondnamed position thereof at a predetermined relative position of said measuring slidewire and its associated contact, and a cumulative indicator operatively connected to said cam for recording successive operations of said barometric switch thereby indicating in discrete steps the altitudev of said barometric switch.

9. A radiosonde measuring system comprising a meteorological measuring unit, a reference unit, a radio transmitter, a barometric switch for connecting said units successively to said transmitter at predetermined altitudes of said switch, a radio receiver for receiving signals from said transmitter, the output of said receiver being a voltage varying with the magnitude, of said quantity being measured, a measuring slidewire and associated contact and a voltage supply therefor, a calibrating slide vire and associated contact for varyingthe voltage. from said voltage supply, a voltage divider connected across said measuring slidewire, a servo system including an amplifier and a switching arrangement therefor, said switching arrangement in one position thereof connecting said measuring slidewire and said receiver output in series opposition across an input circuit of said amplifier and connecting the output of said amplifier to cause said servo system to adjust relatively said measu 'ing slidewire and its associated contact to make the voltage or" the latter equal to said receiver output, said switching'arrangement in another position thereof connecting said receiver output and the output of said voltage divider in series opposition across said input circuit'of said amplifier and connecting the output of said amplifier to cause said servo system-to adjust relatively said calibrating slidewire and its associated contact to make the voltage of said output of said voltage divider equal to said receiver output, said switching arrangement in a third position thereof connecting said measuring slidewire contact and said output of said voltage divider in series opposition across said input of said amplifier and connecting the output of said amplifier to cause said scrvo'system to adjust relatively said measuring slidewire and its asscciated contact to make the voltage of the latter equal to the voltage of said output of said voltage divider, a cam movable with said contact associated with said measuring slidewire for shifting for a predet rmined time said switching ar rangement from said first-named position thereof to said second-named position thereof at a predetermined relative position of said measuring slidewire and its associated contact, said switching arrangement after said predetermined time automatically returning to its said firstnamed position subject to being immediately reshifted to its secondmamed position if said contact is then in said predetermined relative position, and a second cam movable with saidconi6 tact-of said measuring slidewire for shifting said switching arrangement to said third-named position upon the occurrence-of a predetermined sequence of relative movements of said measuringslidewire and its associated contact.

10. A radiosondemeasuring system comprising a plurality of meteorological measuring units, a reference unit, a radio transmitter, a barometricswitch for connecting said units successively to said transmitter at predetermined altitudes of said switch, a radio receiver for receiving signals from said transmitter, the output of said receiver being a-voltage varying with the magnitude of the said quantity being measured, a measuring slidewire and associated contact and a voltage supply therefor, a calibrating slidewire and associated contact for varying the voltage from said voltage supply, a voltage divider connected across said measuring slidewire, a, servo system including an amplifier and a switching arrangement therefor, said switching arrangement in one position thereof connecting said measuring slidewire and said receiver output. in series opposition across an inputicircuit of said amplifier and connecting the output of said amplifier to cause said servo system to adjust relatively said measuring slidewire and its associated contact to makethe voltage of the latter equal to said receiver output, said switching arrangement in another position thereof connecting said receiver output and the output of said voltage divider in series opposition across said input circuit of said amplifier and connecting the output of said amplifiercto cause said servo. system to adjust relatively said calibrating slidewire and its associated contact to make the voltage of said output of said voltage divider equal to said receiver output, said switching arrangement in a third position thereof connecting said measuring slidewire contact and said output of said voltage divider in series oppositionacross said input of said amplifier and connecting the output of said amplifier to cause said servo system to adjust relatively said measuring slidewire and its associated contact to make the voltage of the latter equal to the voltage of said output of said voltage divider, a cam movable with said contact associated with said measuring slidewire for shifting for a predetermined time said switching arrangement from said firstnamed position thereof to said second-named position thereof at a predetermined relative position of said measuring slidwire and its associated contact, said switching arrangement after said predetermined time automatically returning to its said first-named position subject to being immediately reshifted to its second-named position if said contact is then in said predetermined relative position, a second cam movable with said contact associated with said measuring slidewire for shifting said switching arrangement to said third-namedpositionupon the occurrence of a predetermined sequence of relative movements of said measuring slidewire and its associated contact, and a cumulative indicator operatively connected to said first-named cam for recording" successive operations of said barometric switch thereby indicating in discrete steps the altitude of said barometric switch.

11. A measuring system comprising a balanceable network including a measuring slidewire, a calibration slidew-ire connected in circuit with said measuring slidewire, circuit controlling means for-app y ng to said network at least one signal varying with the magnitude of a condi- 17 tion for unbalancing said network, means responsive to the unbalance of said network for adjusting said measuring slidewire in a direction and to an extent sufficient to rebalance said network, actuating means for said circuit-controlling means operable upon substantially fu1lrange relative movement between said measuring slidewire and its associated contact for connecting said rebalancing means between the applied signal and a fixed voltage point with respect to said measuring slidewire, and means responsive to the unbalance of said network for adjusting said calibration slidewire in a direction and to an extent to vary the potential of said point to rebalance the network thereby to provide a standardizing operation with respect to said signal which produced said substantially full-range movement of said measuring slidewire.

GEORGE E. BEGGS, JR. ALFRED W. KOZAK.

References Cited in the file of this patent Number UNITED STATES PATENTS Name Date Arcioni Oct. 1, 1901 Grant Apr. 6, 1937 Barnes Feb. 6, 1945 Schmitt July 30, 1946 Hawes Apr. 15, 1947 Caldwell et al. July 15, 1947 Belcher July 27, 1948 Ingram Oct. 19, 1948 Hanson Nov. 14, 1950 Broomell, Jr. Dec. 11, 1951 

